The present age of a father is equal to sum of ages of his son and daughter. Ten years ago from now, the age of the father was double the age of the son and four times the age of the daughter. The total present age of the father, daughter and son is ____ years.
- AOption (a)
120
- BOption (b)
80
- COption (c)
100
- DOption (d)
60
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Correct answer
100
Why this answer is correct
Shortcut Trick
Let Father's age 10 years ago be x. Then Son's age was x/2 and Daughter's age was x/4.
Present ages: Father = (x + 10), Son = (x/2 + 10), Daughter = (x/4 + 10).
Given: Present Father = Son + Daughter ⇒ (x + 10) = (x/2 + 10) + (x/4 + 10).
⇒ x + 10 = 3x/4 + 20 ⇒ x/4 = 10 ⇒ x = 40.
Present Father = 50. Since Total = Father + (Son + Daughter) and Father = Son + Daughter, Total = 2 × Father = 2 × 50 = 100.
∴ The correct answer is 100 years.
Alternate Method
Let the present ages of the Father, Son, and Daughter be F, S, and D respectively.
Given:
-
F = S + D
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10 years ago: (F − 10) = 2(S − 10) and (F − 10) = 4(D − 10)
From the second condition:
⇒ F − 10 = 2S − 20 ⇒ 2S = F + 10 ⇒ S = (F + 10) ÷ 2
⇒ F − 10 = 4D − 40 ⇒ 4D = F + 30 ⇒ D = (F + 30) ÷ 4
Substitute S and D in the first equation:
⇒ F = [(F + 10) ÷ 2] + [(F + 30) ÷ 4]
Multiply the entire equation by 4 to clear denominators:
⇒ 4F = 2(F + 10) + (F + 30)
⇒ 4F = 2F + 20 + F + 30
⇒ 4F = 3F + 50
⇒ F = 50 years
Calculating S and D:
⇒ S = (50 + 10) ÷ 2 = 30 years
⇒ D = (50 + 30) ÷ 4 = 20 years
Total Age:
⇒ Total = F + S + D = 50 + 30 + 20 = 100 years.
∴ The correct answer is 100 years.
Additional Information
Constant Age Difference
The difference between the ages of two individuals remains constant at any point in time (past, present, or future).
Time Shift in Ages
If the current age is x, then age n years ago was (x − n) and age n years hence will be (x + n).
Ratio and Units Method
When ratios at two different times are given, ensure the ratio difference between the periods is scaled to match the actual time gap.